1. Field of the Invention
The present invention relates to a traction controlling apparatus for a multi-axle vehicle. More particularly, the present invention relates to a traction controlling apparatus for a multi-axle vehicle having air-over hydraulic type anti-lock brakes.
2.Discussion of the Related Art
Some large vehicles are designed with a single front axle and double rear axles to uniformly distribute a load acting on the vehicle. In recent years, there has been a tendency to install anti-lock brakes on such multi-axle vehicle to prevent the wheels from locking when braking. Additionally, to prevent the driving wheels from slipping when accelerating, a traction controlling apparatus is installed on the multi-axle vehicle.
Multi-axle vehicles having anti-lock brakes and a traction controlling apparatus, as shown in FIG. 4, have been known. This drawing shows a plurality of signal lines on the vehicle. Signal lines represented by fine hatched lines illustrate a pneumatic signal system; signal lines represented by bold hatched lines illustrate a pneumatic working system; and signal lines represented by non-hatched lines illustrate a hydraulic system. Although an air pressure supply source is not shown in the drawing, air pressure inputs are represented by arrow marks A.
The vehicle includes a brake valve 100 supplying an air pressure, corresponding to a quantity of brake actuation (not shown), to two relay valves 101 and 101a. Relay valve 101 outputs the air pressure to air master cylinders 104 associated with driving wheels M and follower wheels RR via two-way valves 103 and air control valves 102.
Relay valve 101a outputs the air pressure to an air master cylinder 104a corresponding to the front wheels F via an air control valve 102a.
The air master cylinders 104 and 104a transform the delivered air pressure into a hydraulic pressure that is transmitted to the corresponding wheel cylinders (WC) 15(L,R), 25(L,R), and 35(L,R) for braking.
Each two-way valve 103(L,R) compares the air pressure transmitted from the relay valve 101 with the air pressure transmitted from a traction control valve 300, and then selectively supplies the higher pressure of the two to the corresponding air master cylinder 104(L,R).
Front wheels F and driving wheels M are each equipped with a rotation sensor S. The air control valves 102(L,R), 102a and the rotation sensors S are electrically connected to an electronic central processing unit (ECU) 200. In response to a signal from the ECU 200, the air control valves 102 and 102a are opened or closed to prevent the corresponding wheel from being locked.
Specifically, when the rotation sensors S detect a reduction in the number of rotations of the wheel due to the wheel locking, the ECU 200 is informed of the reduction, and then ECU 200 controls the air pressure in each of the air master cylinders 104(L,R) and 104a via the air control valves 102(L,R) and 102a to check the corresponding wheel from locking.
A general structure of the air-over hydraulic type anti-lock brake has been described above. In addition to the foregoing equipment, the vehicle is additionally equipped with a traction controlling apparatus.
Specifically, the traction controlling apparatus is constructed such that when the ECU 200 detects that the driving wheels M are excessively rotating, the traction control valve 300 is opened, and an air pressure is supplied to the air master cylinders 104(L,R) via two-way valves 103(L,R) and air control valves 102(L,R) to brake the driving wheels M and follower wheels RR.
Only an axle 1 is a driven axle; an axle 2 is a follower axle. Due to this fact, the follower wheels RR tend to lock during traction controlling because both the driving wheels M and the follower wheels RR are simultaneously braked. The locking of follower wheels RR may lead to a further increase of slippage in the driving wheels M.
A traction controlling apparatus shown in FIG. 5 is a typical traction controlling apparatus wherein the follower wheels RR are not braked during traction controlling. Incidentally, the components in FIG. 5 that are the same as those shown in FIG. 4 are designated by the same reference numerals.
Specifically, the traction controlling apparatus shown in FIG. 5 is constructed such that only the driving wheels M are braked during traction controlling. As for braking, the follower wheels RR are braked by the air pressure supplied from the air master cylinder 104a common to the front wheels F.
With the traction controlling apparatus shown in FIG. 5, the increased slippage of driving wheels M, due to the locking of follower wheels RR, does not occur during traction controlling. But, during anti-lock brake controlling when only the front wheels are locked, the front wheels F and the follower wheels RR are controlled together, thus resulting in the follower wheels RR locking because of the variation of the weight borne by the rear axles induced by displacement of the gravity center of the vehicle at the time of quick braking on a road surface having a high friction coefficient such as a road paved with asphalt or the like.
To solve the problems inherent to the three-channel traction controlling apparatuses mentioned above, a traction-controlling apparatus shown in FIG. 6 has been known. This traction controlling apparatus has a pair of front wheels controlled by a common channel and each rear wheel controlled by an independent channel. With this construction, only the locking wheels are controlled by anti-lock braking, and, moreover, only the driving wheels experiencing slippage are controlled by traction controlling.
But, because the traction controlling apparatus shown in FIG. 6 has five channels, the number of components is increased compared with the three channel type traction controlling apparatus. Thus, the five-channel traction controlling apparatus costs more than the three-channel traction controlling apparatus to fabricate.